Concentration of 1, 2, 4-trichlorobenzene



United States Patent 1 2,725,407 CONCENTRATION OF 1,2,4-TRICHLOROBENZENE Alfred J. Kolka, Birmingham, Mich., assignor to Ethyl Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application July 31, 1952, Serial No. 301,971 3 Claims. (Cl. 260-650) The present invention relates -to the concentration of 1,2,4-trichlorobenzene, particularly from mixtures containing minor quantities of 1,2,3-trichlorobenzene with or without other related materials.

1,2,4-trichlorobenzene is a relatively valuable intermediate for the manufacture of polychlorophenoxyacetic acid type plant growth controlling agents. One convenient source of this intermediate is from insecticidally inactive benzene hexachloride isomers. Such isomers are readily dehydrohalogenated and thereby directly and conveniently converted to trichlorobenzenes in large yields.

Unfortunately, the trichlorobenzenes formed in this manner contain appreciable quantities of 1,2,3-trichlorobenzene which interferes with certain polychlorophenoxyacetic acid synthesis techniques.

The desired 1,2,4-isomer can be recovered from the mixture in good yields as by fractionally distilling the mixture inasmuch as its boiling point is about 7 away from that of the 1,2,3-isomer. However, both boiling points are over 200 C. so that the distillation is unwieldy and relatively expensive.

Among the objects of the present invention is the avoidance of the above and related difficulties.

Further objects of the present invention include the provision of a concentrating technique by which a mixture containing 1,2,4-trichlorobenzene and a minor amount of 1,2,3-trichlorobenzene is partially sulfonated.

The above as well as still further objects of the present invention will be more clearly understood from the following description of several of its exemplifications.

According to the present invention, 1,2,4-trichlorobenzene can be readily concentrated from mixtures containing minor quantities of 1,2,3-trichlorobenzene by fractionally sulfonating the mixture to cause the different isomers to sulfonate disproportionately, after which the unsulfonated material is separated to provide the desired concentrate.

Even though these isomers sulfonate at about the same velocity and in many cases the desired isomer sulfonates even somewhat faster than the undesired isomer, the concentration step is quite effective, particularly where there is initially at least a two-to-one ratio of desired to undesired isomer.

As an example of the effectiveness of the process, a mixture of trichlorobenzenes, as commercially available and having by weight 24.7%- of the 1,2,3-isomer, 68.4% of the 1,2,4-isomer, with the remainder a mixture of other chlorinated benzenes, was heated with an equal weight of 100% anhydrous sulfuric acid to a temperature of 113 C. While this temperature was maintained, additional quantities of fuming sulfuric acid containing S03 was added until the total S03 content was equivalent to that required for sulfonating all the 1,2,3-isomer that was present. The reaction was continued for a total time of 4 /2 hours, with stirring, after which the reaction mixture was allowed to cool. In cooling, the mixture separated into two layers, the upper of which was unreacted chlorobenzenes, and this layer was removed by decantation. Analysis of the upper layer showed that it contained by weight 15.1% of the 1,2,3-isomer, 73.7% of the 1,2,4- isomer, and 11.2% of other chlorinated benzencs. The overall yield of the upper layer was about 65% by weight.

As another example of the process of the present invention, sulfonation can be effected with anhydrous sul- 2,725,407 Patented Nov. 29, 1955 furic acid not containing excess S03, the reaction temperature for this purpose being C. or higher. Thus, at C., the above commercial mixture of trichlorobenzenes can be fractionally sulfonated to the extent of about 15 by Weight to thereby leave an unreacted concentrate containing 74.4% by weight of the desired 1,2,4-isomer.

The sulfonating agent can also be sulfuric acid containing smaller or larger amounts of dissolved S03, or it can be an entirely different agent such as chlorosulfonic acid. Sulfonation auxiliaries such as silver sulfate and mercuric sulfate need not be present. The amount of sulfonating agent used is not critical and can be varied with or without adjustments in temperature and/ or time of reaction. For best results the sulfonation should be theoretically sutficient to convert at least half of the undesired isomer, although this amount will actually be divided between the undesired and desired isomers. The reaction should be held down to the point where not more than about 35 to 40% of the total amount of combined isomers is sulfonated.

Although the sulfonation reaction according to the present invention is only partial and may leave an appreciable amount of the 1,2,3-isomer unreacted, nevertheless, isomeric starting mixtures having a preponderance of the 1,2,4-isomer are effectively concentrated in this isomer to the strength of about 75% by weight. At such strengths, the concentrated material offers very little difficulty in the Way of further conversion of trichlorophenoxy acetic acids.

In addition to the above, the sulfonated material formed during the reaction of the present invention can be isolated and purified if desired. Such sulfonated compounds are also useful as intermediates.

One effective technique for recovering the sulfonated material is to take the lower layer of reaction mixture after it has been cooled and dilute with Water until the free sulfuric acid content drops to about 60% by weight. This causes the precipitation of asbestos-like crystals which can be filtered off and washed with cold chloroform. The washed materials can also be recrystallized from chloroform and after recrystallization show a melt-' ing point of 153155 C.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope hereof, it is to be understood that the invention is not limited to the specific embodiments hereof except as defined in the appended claims.

I claim:

1. A method of concentrating 1,2,4-trichlorobenzene from mixtures containing 1,2,3-trichlorobenzene in a concentration of not greater than one mole per two moles of 1,2,4-trichlorobenzene comprising reacting said mixture at a temperature above about 113 C. with anhydrous sulfuric acid whereby the difierent trichlorobenzenes are disproportionately sulfonated, the quantity of sulfonating agent employed being insufiicient to sulfonate all of the trichlorobenzene mixture but at least suflicient to theoretically convert /2 of the 1,2,3-trichlorobenzene, and then separating the unsulfonated material from the sulfonated material to provide the desired concentrate.

2. The method of claim 1 wherein said sulfuric acid contains dissolved S03.

3. The method of claim 1 wherein a total of between about 3540 percent of said trichlorobenzene mixture is sulfonated.

References Cited in the file of this patent UNITED STATES PATENTS 1,766,747 Herz et a1 June 24, 1930 2,511,166 Manske et al. 1 June 13, 1950 2,523,707 Miller Sept. 26, 1950 

1. A METHOD OF CONCENTRATING 1,2,4-TRICHLOROBENZENE FROM MIXTURES CONTAINNG 1,2,3-TRICHLOROBENZENE IN A CONCENTRATION OF NOT GREATER THAN ONE MOLE PER TWO MOLES OF 1,2,4-TRICHLOROBENZENE COMPRISING REACTING SAID MIXTURE AT A TEMPERATURE ABOVE ABOUT 113* C. WITH ANHYDROUS SULFURIC ACID WHEREBY THE DIFFERENT TRICHLOROBENZENES ARE DISPROPORTIONATELY SULFONATED, THE QUANTITY OF SULFONATING AGENT EMPLOYED BEING INSUFFICIENT TO SULFONATE ALL OF THE TRICHLOROBENZENE MIXTURE BUT AT LEAST SUFFICIENT TO THEORETICALLY COVERT 1/2 OF THE 1,2,3-TRICHLOROBENZENE, AND THEN SEPARATING THE UNSULFONATED MATERIAL FROM THE SULFONATED MATERIAL TO PROVIDE THE DESIRED CONCENTRATE. 